Superabsorbent particles and fluff are used in disposable personal care products such as diapers and training pants. Current commercial superabsorbents are typically comprised of a single polymer such as, for example, neutralized polyacrylic acid, hydrolyzed starch-acrylonitrile graft polymer, partially neutralized starch-acrylonitrile graft polymer, and saponified vinyl acetate-acrylic ester copolymers. Although current commercial superabsorbent particles and fluff provide the necessary absorbency, they typically have a glass transition temperature above room temperature. Superabsorbent compositions with an above room temperature glass transition temperature are rigid and brittle at room temperature, the typical temperature of use.
Rigid and brittle superabsorbent compositions are problematic for numerous reasons. During diaper production rigid superabsorbent particles are prone to poke through the surrounding carrier tissue layer and can cause abrasion damage to the polyolefin outer cover films, rendering the diaper unfit for use or sale. Also brittle superabsorbent particles can fragment during production leading to dust or fragment penetration of the inner lining during use.
In addition to the above problems, superabsorbent particles are not bonded in current commercial composites and the superabsorbent is therefore mobile. This mobility can cause a change in the distribution of the superabsorbent during the assembling process or during shipping prior to use. The resulting disposable personal care products will not provide the desired absorbency and may result in leakage.
Interparticle bonded aggregates of superabsorbent particles have been developed to solve the problem of superabsorbent particles mobility. Such aggregate macrostructures are disclosed in Roe et al., U.S. Pat. No. 5,102,597, and Rezai et al., U.S. Pat. No. 5,324,561. Although bonded superabsorbent particle aggregates decreases mobility of the particles, this solution results in undesired surface non-uniformity and a lengthy production process. Another solution, disclosed in Allen et al., U.S. Pat. No. 4,861,539, is to cast a superabsorbent precursor into a film which is subsequently crosslinked to form a solid superabsorbent film. This solution also has its deficiencies in that the film is nonporous and has poor liquid transport properties and is prone to gel-blocking.
There is a need or desire in the industry to create a softer, less brittle superabsorbent composite and a superabsorbent film that has good liquid transport properties that is not prone to gel-blocking.